Variable transformer



June 10, 1911. J E|TMAN ET AL 2,245,266

VARIABLE TRANSFORMER Filed Sept. 13, 195g '2 sheets-sheet 1 fig 38 InnerCoil H---Hinimum Speed Outer- Coil Maximum Speed Joseph F Eitman.

Elmer- J. Zelt, Armin F. Mitter'maien Then" Attorney.

Inventors= Patented June 10, 1941 VARIABLE TRANSFORMER Joseph F. Eitman,Elme r J. Zelt, and Armin F.

Mittermaier, Fort Wayne, Ind., assignors to General Electric Company, acorporation of N ew York Application September 13, 1938, Serial N 0.229,726 (Cl. 171-119) 12 Claims.

This invention relates to variable transformers and more particularly toimprovements in the construction of variable transformers of the type inwhich a movable brush makes contact with the transformer winding. I

By the term variable transformer, wemean either a conventionaltransformer, or an autotransformer or a reactor whose eifective numberof winding turns is variable. A reactor is properly included becausestructurally it is like a transformer, the primary difference beingmerely one of function or use. I

In a well-known form of a variable transformer of this type the-core istoroidal in shape and the brush is rotated about the axis of the core.In this manner struction is provided.

In accordance with this invention the construction is improved andsimplified in a number of particulars.

An object of the invention is to provide a new and improved variabletransformer.

Another object of the invention is to provide a variable transformer, ofthe type in which a brush slides on the inner surface of a toroidalwinding, with means for causing the conductors of said winding to liesubstantially in a cylindrical surface along the brush path.

Anotherobject of the invention is to provide a new and improvedarrangement for supporting and confining the brush pigtail.

a simple and compact con- A further object of the invention is toprovide novel and simple means for adjusting the limits of brush travel.

An additional object of the invention is to provide a new and improvedway of placing a twolayer variable autotransformer winding on a toroidalcore. f

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawings and itsscope will bepointed out in the appended claims.

In thedrawings, in which similar reference characters designate th sameelements throughout the several views, Fig. 1 is a front view of thevariable transformer with the cover in place, Fig.

2 is a circuit-diagram oi the transformer connected as a speedcontroller for the split-phase motor, Fig. 3 is a modification of Fig. 2in which the transformer winding is placed on the core in a novel mannerso as to secure rated voltage on both motor windings, Fig. 4 is a viewsimilar to Fig. l with part of the cover and supporting means brokenaway, Fig. 5 is a sectional view along the line 5-5 of Fig. 4, and Fig.6 is a detailed so-called exploded view of the adjustable means forlimiting the range of brush travel.

Referring now to the drawings and more particularly to Figs. 4 and 5,the transformer is mounted in a casing I. This casing is in the form ofa conduit or outlet box and is provided with knockouts 2 through. whichconnections can be made to the transformer as desired. Brackets 3fastened to th inside of the casing in any suitable manner such as bywelding or soldering, provide means for fastening the transformer in thecasing. The transformer consists essentially of a toroidal core 4 whichis preferably, although not necessarily, of wound instead of discconstruction and a winding 5 thereon. Winding 5 is shown, by way ofexample, as consisting of two layers. This coil and core assembly isclamped between a supporting strap 6 and a front strip 1 by means ofscrews 8. Screen 8', passing through clearance holes in members 6 and 1,are threaded into brackets 3 for holding the assembly in the casing.Suitable insulation 9 and I0 is placed between the winding 5 and thesupporting members 8 and I. For making contact with the inner surface ofthe winding so as to vary the transformer ratio is a brush or slidablecontact I l'.

It has been found that it is difiicult to place the winding 5 on thecore in such a way that all of the conductors will lie evenly and thisdifliculty is accentuated when the winding is clamped in a support, asthe clamping action tends to buckle some of the turns and thus producean uneven arrangement of the turns. 'I'hlS makes it difilcult for thebrush to slide evently in the winding.-

In order to overcome this difliculty there is provided what is referredto as a wire retainer II. This wire retainer is preferably made ofinsulated material, such for example as the synthetic resin known asBakelite and .is shown in the form of a circular cup-shape member. Thiswire retainer is pushed through the opening in the toroidal winding fromth front to the back, thereby smoothing out the inner surface of thewinding and forcing all of the inner conductors of the winding to liesubstantially in a cylindrical The wire retainer I2 is provided with anopening which is concentric with the axis of the toroidal core andwinding and this opening acts as a bearing support for the shank l5 oithe brushholder.

The brushholder is provided with an internal passageway 16 forconducting the brush pigtail I! to the back of the wire retainer l2.After it has passed through the wire retainer the pigtail' is wrappedone or more times around the shank l5 of the brushholder, so as toprovide enough slack to permit rotation of the brushholder. Its end isthen fastened to a lead l8, the end of which is clamped between apigtail retainer!!! and the wire retainer l2.

The other bearing support for the brushholder is provided for by anopening in the strip 1 and the brushholder is prevented from axialmovement by suitable flanges 20 formed thereon.

The outer flange 29 is provided with a lug or projection 2| whichcooperates with a stop 22 formed by pressing inwardly a finger 22 formedout of the strip 1. This construction automatically limits the maximumangle through which the brush can be rotated and prevents the brush fromfalling into a space 23 between the ends of the outer layer of thewinding 5.

Often it is desirable, however, to prevent the brush from being rotatedthrough this maximum angle, so as for example to prevent the applicationof overvoltage to a device connected to the output of the transformer.This limitation of the brush travel to any desired portion of itsmaximum range of travel is secured by a novel construction consisting ofa pair index plates 24 and 25. These plates haveoircular openingsprovided with teeth which engage a set of teeth 26 of the brushholder.Thus, the index plates may be rotated through any desired relative angleand then fitted onto the brushholder into engagement with the teeth 26which will then lock them in this relative angular relationship. Theyare retained in position by means of a split or prong-shape spring'member-flwhich fits into a groove in the brushholder. Projections onthe plates 24 and cooperate with an upset stop member 2 8v formed in thestrip I.

The circuit of the transformer is controlled by a switch 29 shown, byway of example, as a conventional toggle-operated snap switch. Itsoperating arm is provided with anotch 30 which is entered by theprojection on the index plate 24 so that when the brush. is movedcounterclockwise to one of its previously set limits the switch 29 willautomatically be opened and as soon as the brushholder is rotated in aclockwise direction so as to move the projection on plate 24 away fromstop 28 the switch 29 will be closed. 'When the brushholder is rotatedin a clockwise direction, the adjustable index plate 25 cooperates withstop 28 to limit the range of the brushholder in this direction.

The front of the casing I is closed by a suitable cover 3| fastenedthereto by means of screws 32 threaded into the brackets 3. Cover plate3| is provided with a dished-in central portion having an openingsurrounding the metal cap l4.

Fitted into this dished-in portion is-an operating handle 33 having afiat-sided extension or shaft 34 which enters the end of the brushholderand which is frictionally retained therein by means of a spring member35 which is pressed between the side of the end opening of thebrushholder and the flat portion of the extension 34 of the handle.

In this manner the handle may readily be removed by merely pulling itout away from the casing. I

' In Fig. 2 the transformer is shown as being provided with three inputleads 36, 31 and 38 and with three output leads 39, I8 and 40. Inputleads 36 and 31 are adapted to be connected to a standard alternatingcurrent circuit of a given voltage and leads 36 and 36 are adapted to beconnected to a similar circuit of double this voltage. The main winding4| of a split phase motor 42 is connected between one of the outputconductors 39 and the brush lead l9, while a capacitor winding 43 forthe motor is'connected between the brush lead l8 and output terminal 40.By sliding the brush ll along the outer coil of the winding 5 therelative voltages of the main and start windings of the motor will bevaried in order to vary the motor speed over a wide range. In Fig. 3 thefundamental circuit is the same as in Fig. 2 except that output lead 40has been connected to input lead 38 instead of to input lead 31. Themotor 42 willbe assumed, for purposes of illustration, to be a standardmotor having a rated voltage of volts. The purpose of the modificationshown in Fig. 3 is toinsure that full 110 volts is applied to both motorwindings when it is started and whenever maximum speed is desirable.Suitable supply circuits for connection between input conductors 36 and31 on the one hand and input conductors 36 and 38 on the' outer layer,which is adapted to operate at 104 volts, thus making up the total 220volts. The reason that the voltage of the inner layer is higher than thevoltage of the outer layer is because it is necessary to provide thespace 23 between the ends of the outer layer so as to prevent anypossibility of the brush 1 i short circuiting the entire outer layer andalso in order to provide proper insulation between the ends of the outerlayer. This also means that only a portion of the outerlayer can be usedfor securing adjustable voltage because the brush must be limited in itsmotion at the ends of the outer layer adjacent the space 23 so as toprevent the brush II from falling into this space. If that happened itwould be dimcult to get the brush on the winding again. Thus, asindicated by way of example in-Fig. 3, there are 2 volt sections on setby the projection 2l and stop 22 the switch I 29 will automatically beopened when the brush H is placed in this maximum speed position andwill automatically be closed as soon as the brush is moved away fromthis position toward the minimum speed position. As will be seen fromFig. 3.'the-voltage applied to both windings 4| and 43 of the motor willbe 110 volts when the brush is in the maximum speed position and that asthe brush is moved toward the minimum speed position the voltage of themain winding is decreased and the voltage of the start winding isincreased. With this arrangement the motor will always be ing a bearingsupport started at maximum voltage and will thus always develop maximumstarting torque.

While there hasbeen shown and described a particular embodiment of thisinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. A variable transformer comprising, in combination, a toroidal core ofmagnetic material having a cylindrical inner surface, a winding on saidcore, a relatively thin circular wire retaining member of insulatingmaterial pressed into the opening of said core for forcing theindividual conductors forming the inner surface of said winding to lieevenly in a substantially cylindrical surface adjacent the inner side ofsaid wire retaining member, a brush for contacting the inner surface ofsaid winding adjacent the inner side of said wire retaining member, arotatable holder for said brush, and an opening in the center of saidcircular wire retainer formfor said brushholder.

2. A variable transformer comprising, in. combination, a toroidal coreof magnetic material having a cylindrical inner sm'face, a winding onsaid core, a relatively thin circular wire retaining member ofinsulatingmaterial pressed into the opening of said core for forcing theindividual conductors forming the inner surface of said winding to lieevenly in a substantially cylindrical unobstructed surface, a movablebrush for engaging said unobstructed surface, a casing for said core andwinding, and means for clamping said winding and core to the innerwalls-of said casing independently of said wire retaining member.

3. A variable transformer comprising, in combination, a toroidal core ofmagnetic material, a winding on said core, a circular wire retainingmember of insulating material pressed into the opening of said core forforcing the individual conductors forming the inner surface of saidwinding to lie 'evenly' in a substantially cylindrical surface, a brushfor contacting the inner surface of said winding, a rotatable holder forsaid brush, an opening in the center of said circular wire retainerforming a bearing support for said brushholder, a passageway in saidbrushholder between said brush and the opposite side of said wireretainer, and a pigtail connection for said brush inserted in saidpassageway.

4. A variable transformer comprising, in combination, a toroidal core ofmagnetic material, a winding on said core, a circular wire retainingmember of insulating material pressed'into the opening of said core forforcing the individual conductors forming the inner surface of saidwinding to lie evenly in a substantially cylindrical surface, a brushfor contacting the inner surface of said winding, a rotatable holder forsaid brush, an opening in the center of said circular wire retainerforming a bearing support for said brushholder, a passageway in saidbrushholder between said brush and the opposite side of said wireretainer, a pigtail connection for said brush inserted in saidpassageway, said pigtail being wound around said brushholder, and apigtail retaining member fastened to said wire retainer and forming aspace therebetween for the coil formed by said pigtail.

5. In a variable transformer of the type comprising a winding and amovable brush slidable across said winding for varying the transformerratio, the combination of a rotatable holder for said brush, said holderhaving asection provided with at least one outwardly extendingprojection, a pair of index members provided with openings having atleast one inwardly extending recess for receiving said projection,extensions on said members, and a stop arranged in the path of rotationof said extensions for limiting the rotation of said brush to apredetermined portion of a complete turn.

6. In a variable transformer of the type comprising a winding and amovable brush slidable across said winding for varying the transformerratio, the combination of a movable holder for said brush, meansincluding an element adjustably positioned on said brushholder forlimiting the motion of said brushholder in one direction to anyparticular point on said winding, means including a separate elementindependently adjustably positioned on said brushholder for limiting themotion of said holder in the opposite direction to any other particularpoint on said winding, and a common locking mechanism on saidbrushholder for both of said adjustable elements.

7. In a variable transformer of the type comprising a winding and amovable brush slidable across said winding for varying the transformerratio, the combination of a rotatable holder for said brush, said holderhaving a circular section provided with a plurality of outwardlyextending teeth, a pair of index plates provided with circular openingsvhaving a plurality of inwardly extending teeth for receiving the teethon said holder, extensions on said index plates, a stop mounted in thepath of rotation of said extensions for limiting the rotation of saidbrushholder to any predetermined portion of a complete turn thereofwhich is determined by the relative settings of said index plates, andmeans for maintaining engagement between the teeth on said index platesand the teeth on said circular section of said brushholder.

8. A variable transformer comprising, in combination, a winding, amovable brush slidable across said winding for varying the transformerratio, a movable holder for said brush, adjustable means for limitingthe motion of said brushholder in one direction to any particular pointon said winding, separate independently adjustable means for limitingthe motion of said holder in the opposite direction to any otherparticular point on said winding, and a switch in circuit with saidtransformer arranged to be actuated by one of said adjustable means inresponse to its rotation by said brushholder.

9. In a variable transformer, a toroidal core, a two-layerserially-connected autotransformer winding on said cor said windinghaving three input leads connected respectively to the terminals of saidwinding and, to the electrical midpoint thereof, a brush slidable acrossthe outer layer of said windings, said winding having three output leadsconnected respectively to the termi- 'nals of saidwinding and to saidbrush, the ends of said outer layer being separated by a spacesuflicient to prevent short circuiting of said outer layer by saidbrush, and means for limitin the motion of said brush toward said spaceso as to prevent said brush from dropping ofi said outer layer into saidspace, one of the limiting positions of said brush correspondingsubstantially to the electrical midpoint of said winding.

10. In combination, an autotransformer having a two-layer winding, theelectrical terminals of said winding being in the inner layer thereof,the electrical midpoint of said winding being in said outer layer, and acontact movable across the outer layer of said winding and having arange of motion which includes contact with'said electrical midpoint.

11. In combination, a transformer provided with a toroidal core, atwo-layer autotransformer winding on said core,- the outer layer of saidwinding having a space between its extremities, the electrical terminalsof said winding being in the inner layer thereof, the electricalmidpoint of said winding being in the outer'layer thereof adjacent tobut not at the edge of said space between the ends .of said outer layer,and a contact movable across the outer layer of said windin and having arange of motion which includes contact with said electrical midpoint.

12. In combination, asingle phase autotransformer having a pairfotoutput terminals connected to the'extremities of its winding, a contactmovable on said winding and having a range of positions which includescontact with the electrical midpoint of said winding, an input circuitfor said transformer, a switch connected in said input circuit, andmeans responsive to the position of said movable contact for openingsaid switch when said contact is in engagement with substantially theelectrical midpoint of said winding and for closing said switch whensaid contact is in any other position.

' JOSEPH F. EITMAN.

EL'NIER J. ZELT. ARMIN F. MITTERMAIER.

